1. Field of the Invention
The invention relates to conveyor systems for handling objects, such as fruit, in which ejector levers are incorporated into a conveyor chain. The invention relates specifically to an apparatus and method for detecting missing ejectors in such a conveyor system and for automatically adjusting the chain stretch of the conveyor as the chain conveyor systems wears.
2. Description of the Prior Art
The sorting, grading, separation and handling of any object such as fruit, and in particular citrus fruits, on conveyor systems in combination with many types of fruit handling apparatus is well known. In one type of conveyor system, the conveyor is comprised of two chains which are driven along each side of a conveyor line. Mounted between the two chains is a plurality of spools for defining pockets between the spools and for spinning the fruit which are nested in the pockets. The fruit is loaded onto the conveyor from a bin or other source and through various conventional means is ultimately sorted so that substantially only one item of fruit lies in the pocket between two adjacent spools on the conveyor line. As the fruit is sorted, graded or otherwise handled, it is necessary to selectively remove the fruit from the conveyor line at designated pockets. The means provided for selective designation includes an ejector finger carried on the conveyor and positioned beneath the pocket between the two spools. Ejector finger is activated at preselected positions according to the fruit sorting, grading or handling application which is being undertaken and selectively rotated to lift or eject the fruit from the pocket into a sorting bin to the side of the conveyor. A description of this type of conveyor may be found in U.S. Pat. No. 5,174,429 assigned to the assignee of the present application, which is expressly incorporated herein by reference.
As it often happens, the conveyor runs at fairly high speeds and for long periods of time. From time to time, an ejector may fail or break. Typical conveyor lines may extend up to 100 feet with an interspool spacing of 3.75 inches. Therefore, it is not uncommon to have as many as 400-800 ejector fingers incorporated within a conveyor line in a typical application. Even if a very small percentage of these fingers are damaged or otherwise fail to operate, the number of fruit which will then be inappropriately processed or not processed at all can become significant over time.
It should also be borne in mind that the conveyor system is an endless loop. Therefore, approximately half the conveyor system is exposed on the top side of the conveyor while the remaining half is disposed under the conveyor line upside down on the return path of the loop. The underside portion of the conveyor system is generally visually and physically difficult to access. Therefore, at any one time only approximately half or less the conveyor and the ejector fingers can be viewed or easily accessed. Should a finger fail, it can be a time consuming task to find which of the pockets contains the malfunctioning or missing ejector finger.
Furthermore, it also must be kept in mind that processing of fruit or other items on the conveyor is based upon a position and time coincidence of the fruit in the conveyor line. The time is usually controlled by an electronic circuit with fixed timing, which is based upon the assumption that there is a certain unit distance or spool-to-spool distance which is substantially constant along the length of the conveyor and during the lifetime of the conveyor. However, in reality each of the elements and parts of the conveyor chain, even when made out of metal, gradually wear and the tolerances of the pieces increase. While the change in any one part is very small, the changes accumulate along the linear length of the chain such that "chain stretch" can be observed. The consequence of chain stretch is that the assumed positions of the pockets between the spools in the conveyor end up in different locations at different times from what originally existed when the conveyor system was new. The conveyor becomes unsynchronized and can begin to malfunction. In some cases chain stretch of as much as an entire pocket length or spool-to-spool distance can occur.
Therefore, what is needed is some type of apparatus and method in which missing or broken ejectors in a conveyor system can be automatically determined and located and wherein chain stretch can be automatically diagnosed and adjusted.